CHAPTER III
RESEARCH METHODOLOGY
3.1
Introduction
For the purpose of this study 6 different type of material was sampled for
laboratory compaction test and a total of 65 numbers of field compaction tests
using the sand replacement method and nuclear densometer method was carried
out, the methodology as in the flow chart was adopted. The samples were
collected at various locations in the “Electrified Double Track Project from
Rawang to Ipoh”. All the samples was marked and taken to the soil laboratory to
carry out the necessary laboratory tests as described in Table 3.1. During the
actual embankment construction work, field compaction test was carried out using
the Nuclear Densometer followed by Sand Replacement approximately 0.15m
away. The bulk density from the Sand Replacement was known, and dry density
was computed after the sample is oven dried and moisture content known whereas
the bulk density, dry density and moisture content was immediately known using
the Nuclear Densometer. The research methodology is shown in the flow chart in
section 3.1.1.
3.1.1
Flow Chart for Research Methodology
Correlation of Nuclear
Density & Sand
Replacement Method
Lab Testing
Calibration of
Equipments
Proctor Tests
Conclusion
Field Test
Sand Replacement
Nuclear Density
Compile Results
Analyze
Conclusion
3.2
Laboratory Tests
In the soil laboratory the following tests in Table 3.1 was carried out.
Table 3.1: Summary of Laboratory tests.
No
Type of Test
Standards used
1
Modified Proctor Test
B.S 1377 : Part 4 : 1990
2
Sand Density
B.S 1377 : Part 9 : 1990
3
Calibration of Sand Cone
B.S 1377 : Part 9 : 1990
3.2.1
Modified Proctor Test
The series is begun with 5kg of the soil in a damp condition somewhat
below the probable optimum moisture content, approximately 5% of the sample
weight. After the first sample was compacted in 5 equal layers in the mold using a
4.5kg hammer at a drop of 450mm, its wet unit weight was taken and a portion of
the sample was placed in a drying oven. When the sample is completely dry, it is
weighed again. The difference between the wet and dry weight yields is the
moisture content that is expressed as a percent of the dry weight.
A second sample with increased moisture content is compared and the
weighing and drying process is repeated. Additional samples with increasing
moisture content are processed until the wet unit weight decreases or the soil
becomes too wet to work.
The dry density and moisture content values for each sample were then
plotted and a smooth curve is formed. The highest point on the curve represents
the maximum dry density and the optimum soil moisture content for that sample.
In other words, that is the absolute laboratory compaction for the amount of
compactive effort used on this particular soil (B.S 1377 : Part 4 : 1990). All the
six samples collected was tested in the same manner and results recorded in
standard test format as in APPENDIX A. The summary of proctor tests are as
tabulated in Table 3.2.
Table 3.2: Summary of Proctor Test results
3.2.2
Sample
Identification
Dry
Density
Mg/m3)
Optimum
Moisture
Content(%)
Silty Clay 1
1.608
23
Silty Clay 2
1.672
18.8
Silty Clay 3
1.692
21.62
Silty Clay 4
1.886
16.5
Sand
1.924
12.5
Crusher-run
2.330
5.1
Calibration of Replacement Sand
The replacement sand used was a clean closely graded silica sand.
The grading of the sand was such that 100 % passed the 600 μm test sieve
and 100 % retained on the 63 μm test sieve. In addition the sand was free
from flakey particles, silt, clay and organic matter. Before the sand was
used it was oven dried and stored in a loosely covered container. A
cylinder of known volume was used to calibrate the replacement sand’s
density. The cylinder was filled with the sand and leveled to the top. The
weight was recorded, this was repeated several times and since the volume
of cylinder is known the density was easily computed (B.S 1377: Part 9 :
1990). The test data is attached in APPENDIX B.
3.2.3
Calibration of Sand Cone
The volume of sand in cone of the pouring cylinder is calibrated using
sand which was calibrated earlier. The pouring cylinder was placed concentrically
on the top of the calibrating container and filled with constant mass of sand. The
shutter on the pouring cylinder was kept closed during this operation. The shutter
was opened and sand allowed to run out, when no further movement of sand of
sand takes place in the cylinder, the shutter was closed. The pouring cylinder was
removed with the remaining sand in it and the mass of sand was weighed and
recorded. The measurements was repeated three times and the mean was taken for
computation (B.S 1377: Part 9 : 1990). The calibration data is attached in
APPENDIX C.
.
3.3
Field Tests
In the field the following tests as in Table 3.3 was carried out.
Table 3.3: Summary of Field Tests
No
Type of Test
Standards Used
1
Sand Replacement method
B.S 1377 : Part 9 : 1990
2
Nuclear Densometer
B.S 1377 : Part 9 : 1990
3.3.1
Field Density using Nuclear Densometer
Site preparation was carried out using the scraper plate to smooth out the
test surface. The scraper plate was placed on the test surface, the drill rod was put
through the extractor tool, then through the scrapper plate guide. Securing the
scraper plate with one foot, hammer was used to drive the drill rod into ground
approximately 0.3m (Figure 3.1). The rod was removed from the ground using the
extractor tool with the remaining foot on the plate. The corners of the plate was
marked using the drill rod. The scrapper plate was then removed and the gauge
was positioned within the outline of the scraper plate. The trigger in the handle
was then released and the source rod lowered to the desired depth. The gauge was
pulled in the direction of the keypad to ensure that the source rod is snug against
the wall of hole. One minute after the start button is pressed the moisture content,
bulk density and dry density is obtained. The field result for all the 65 number of
test recorded in the standard format as in APPENDIX D.
Figure 3.1: Drill rod driven into ground.
Figure 3.2: Lowering of source rod.
3.3.2
Field Density using Sand Replacement method
The unit’s base plate is laid on the compacted surface and material is
excavated through the hole in the plate to a depth of about 150 mm (Figure 3.3).
This wet material is weighed, dried in an oven and weighed again to determine
the moisture content.
The volume of the hole is measured by filling it with dry, free-flowing
sand from a special sand-cone cylinder (Figure 3.4).Since the density of the sand
is known, the volume of the hole was calculated. The density (wet unit weight) of
the compacted sample is found by dividing the weight of the material by the
volume of the hole. Dry unit weight was found by dividing the wet unit weight by
one plus the moisture content expressed as a decimal. The field result for all the
65 number of test recorded in the standard format as in APPENDIX E.
Figure 3.3: Material excavated through hole in base plate.
Figure 3.4: Sand in the pouring cylinder being released.
3.4
Analyzing of Results
The field density results obtained will be analyzed using the mathematical
(statistical) and graphical method. The field compaction density Nuclear
Densometer method is recorded as Xi and the field compaction density obtained
using sand replacement method at the same location is recorded as Yi. The results
of Xi and Yi is entered on the standard format and computed is as in APPENDIX
F. The following data is computed:-
i.
The sum of Xi (∑X), sum of Xi2 (X2), sum of Yi (∑Y), sum of Yi2 (Y2),
and the sum of XiYi (∑XY).
ii.
The average in place density by Nuclear Densometer ( X )is calculated .
X=
X
(3.1)
n
where n = number of tests
iii.
The average in place density by Sand Replacement method ( Y ) is
calculated.
Y=
iv.
Y
(3.2)
n
The regression coefficient is calculated (r).
r=
Sxy
Sxx Syy
where Sxy =
Syy =
i.
(3.3)
 XY   X Y   n , Sxx =  X    X 
Y   Y 
2
2
2
2
n

The Adjusted Nuclear Density (Y).
Y= b Xi + a
(3.4)
 n ,
where b =
Sxy
, a = Y  bX
Sxx
The value of the coefficient of correlation r shall always lie between +1
and -1. When r = +1, then there is perfect positive correlation between the
variables. When r = -1, then there is a perfect negative correlation. Preferably if
the value lies above + 0.8, hence a high degree of correlation exists between the
two variables.